The invention relates to interposer assemblies used for forming electrical connections between spaced contact pads on circuit members.
Interposer assemblies are used for forming electrical connections between densely spaced contact pads on adjacent parallel circuit members. Commonly, the circuit members are a circuit board and a ceramic plate carrying integrated circuits. The pads on the members are arranged in identical patterns.
The interposer assembly includes an insulating plate and a plurality of through-contacts carried in the plate and arranged in the same pattern as the pads on the circuit members. The assembly is sandwiched between upper and lower circuit members to form electrical connections between opposed pairs of contact pads.
In one type of interposer assembly, the lower circuit member is permanently held against the bottom side of the plate before the upper circuit member is pressed against the plate. The contact pads on the lower circuit member are soldered to the contacts. This enables the interposer assembly and lower circuit member to form a subassembly that is assembled later with the upper circuit member to interconnect the circuit members.
The contact pads on the lower circuit member each include a solder layer to form the soldered connections. The lower circuit member is pressed against the bottom side of the plate with the solder layer on the pads engaging the contacts. The lower circuit member and interposer plate are placed in a reflow oven to melt the solder layer and solder the contacts and contact pads together. The solder connections form reliable mechanical and electrical connections between the contacts and contact pads and hold the lower circuit member firmly against the plate.
The contacts project above the top surface of the plate of the soldered subassembly. The upper circuit member is pressed against the upper side of the plate with the contact pads on the upper member engaging the contacts. The upper circuit member is held against the plate with the contacts forming electric connections between aligned pairs of pads.
Interposer assemblies form electrical connections between contact pads arranged in very close proximity to each other. The pads may be arranged on a one millimeter center-to-center grid. A number of interposer assemblies may be mounted on a single frame, with thousands of contacts in the frame. In addition to requiring closely spaced contacts, the contacts must make reliable electrical connections with the pads when the assemblies are sandwiched between the circuit members. Failure of a single contact to make a reliable connection renders the entire frame useless.
A low mechanical closure force is required in order to prevent undue stress on a ceramic circuit member. A high closure force could distort or possibly break the ceramic member. Further, interposer assemblies must occupy a minimum width between the circuit members. The contacts must compress and enable the circuit members to be flush against the plate. The contacts must be compliant or resilient enough to deform with a lower closing force and yet must be sufficiently stiff to establish reliable electrical connections between pairs of contact pads.
Conventional interposer assemblies in which one circuit member is soldered to contact pads have contacts that are relatively rigid after being soldered to the contact pads. A high closing force is required to press the other circuit member flush against the interposer plate.
On occasion it may be necessary to replace a circuit member with a substitute circuit member if a defect were found after pressing the circuit member against the interposer plate. The is compressed contacts do not have sufficient resiliency to return to their original projections above the plate after removal of the circuit member. Reengagement of the contacts with the contact pads of the substitute circuit member often results in failure of one or more contacts to form electrical connections.
The invention is an improved interposer assembly including metal through contacts confined in closely spaced passages extending through an insulating plate. The contacts have resilient upper and lower contact arms that space contact surfaces away from opposite sides of the plate. The contact arms can be compressed against contact pads of circuit members with a low closing force. However, the contact arms are sufficiently resilient to return the contact surfaces away from the plate for reengagement with contact pads if necessary to permit adjustment or replacement of the circuit member.
The upper and lower contact arms of each contact are compressed by the contact pads independently of one another. This permits the contact pads of one circuit member to be soldered to the contact arms on one side of the plate prior to assembly of the interposer assembly with the other circuit member. The compression of the contact arms by the one circuit member does not affect the resiliency and shape of the contact arms on the other side of the plate. The contact arms on the opposite side of the plate remain in position to form reliable pressure connections or solder connections with the contact pads of the other circuit member.
An interposer assembly having features of the present invention includes an insulated plate and a number of metal contacts carried in the plate. The plate is formed from a single piece of insulating material. A number of single contact passages are in the plate, each contact passage including a slot extending through the thickness of the plate, an upper recess extending away from the slot and open to the top surface of the plate, and a lower recess extending away from the slot and open to the bottom surface of the plate. The slot includes a nominal width portion extending from the top surface of the plate and a reduced width portion extending from the bottom surface of the plate. A transverse wall joins the slot portions.
Each contact includes a body portion in a passage slot, with upper and lower contact arms extending from the body portion. A contact surface is on each contact arm, the distance between the contact surfaces greater than the thickness of the plate when the contact arms are unstressed. The contact body portion has a nominal width portion in the nominal width portion of the slot and a reduced width portion in the reduced width portion of the slot and includes an abutment surface abutting the transverse wall of the slot to locate the contact in the contact passage. The upper contact arm extends into the upper recess and overlies a recessed floor of the upper recess and the lower contact arm extends into the lower recess and overlies the floor of the lower recess of the passage.
When a circuit member is pressed against the lower contact arms, each contact arm engages the floor of the lower recess to maintain the position of the contact in the passage slot. This enables the sets of upper and lower contact arms to be deflected essentially independently of one another.
The compressed contact arms move entirely within the upper and lower recesses when the plate is compressed between circuit members. The lower set of recesses is sized to accommodate solder connections in the recesses to enable soldering of the lower contact arms to contact pads. Preferably the upper recesses are also sized to accommodate solder connections in the recesses. This permits identical plates to be used having contacts with upper contact arms configured to form pressure connections or upper contact arms configured to form solder connections to electrically connect with contact pads.